There are many applications in which it is desirable or necessary to protect electrical equipment from the harmful effects of large amplitude, fast rise-time voltage transients. These transients may be due, for example, to lightning, power interruptions, static discharge or other similar phenomena, and have amplitudes of up to 2500 volts and rise times of a few nanoseconds. If these transients are not suppressed, it is possible for voltages and currents of excessively large value to be coupled to sensitive electrical equipment and to cause permanent damage thereto, especially if the equipment utilizes integrated circuits, MOS (metal oxide silicon) devices, hybrid devices, and other voltage or current sensitive semiconductor devices and components.
Heretofore, it has been common practice to protect electrical equipment from the damaging effects of voltage transients by using band pass filters or spark gap devices. Band pass filters have the disadvantage of not offering protection against transients in the UHF band (225-400 Mhz), and spark gap devices either do not respond quickly enough, especially in the UHF band, or have a high insertion loss at UHF frequencies. Because of the finite response time of spark gap devices, generally measured in microseconds, it is therefore quite possible and likely that a transient having a very fast rise time, for example, of the order of nanoseconds, will pass by the spark gaps of these devices without being suppressed thereby.